Geostrophic current estimation using altimetric cross-track method in northwest Pacific

Abstract

Geostrophic current contributes a large part of ocean current, which plays an important role in global climate change. Based on classic oceanography, geostrophic current can be derived from pressure gradient. Assuming water density to be constant, we can estimate geostrophic current from Absolute Dynamic Topography (ADT). In this paper, we use ADT data obtained from multi-satellite altimeter to extract sea surface tilt along track at ground track crossover points. The calculated tilt along these two tracks can be converted into orthogonal directions and are used to estimate geostrophic current. In northwest Pacific, geostrophic current velocities computed above are evaluated using Argos data, a global Langrangian drifter program. 771 precisely temporal and spatial coherent Argos data with estimated geostrophic velocity data are used for evaluating. Effect of different threshold length of the low pass filter applied to ADT is discussed. A threshold length of 75 km is most suitable for the study area. The estimated geostrophic velocity and the Argos measurement agree well with each other, with correlation coefficient R equals 0.867 for zonal component, and 0.734 for meridional component. A relationship between the estimated geostrophic velocity and Argos measurement is drawn.